Use logical marker to indicate an ordered row filter

[MarcusKlik]

If a back-end can assume the row filter is ordered, it doesn't need to order the vector before starting a sequential read.

[MarcusKlik]

A row-selection of the form:

ft[Year > 2007, }

will not change the order of the selected rows. The proposed ordering flag will signal this. Any subsequent read of the selected rows (by the back-end) can be done sequentially.

[MarcusKlik]

row-ordering flag was added in 67fe33a